and coverage increases through early summer as individuals grow. By late summer, barnacle coverage 

 decreases, as individuals are lost to predation (especially in Zone 3), or desiccation (especially in Zone 1). 

 Barnacles may settle so densely or grow so quickly that they may eventually be lost to intraspecific 

 competition. Crowding and 'hummocking' (cf. Grant 1977) weakens an individuals attachment to sub- 

 stratum, and clumps of barnacles may be lost, especially during autumn storms (Foertch and Keser 1981). 

 Algae that have settled and grown on or between barnacles may also be lost with the removal of barnacles. 

 Another factor contributing to local barnacle mortality is predation; the most important predators in the 

 Millstone Pomt area are two carnivorous snails, Urosalpinx cinerea (oyster drill) and Thais lapillus (dog 

 whelk). These snails are most abundant in late summer, and are partially responsible for the decline in 

 barnacle abundance (cf. Hanks 1957; Bayne and ScuUard 1978; Foertch and Keser 1981). 



Barnacles are also lost as a consequence of thermal stress. Throughout the NUEl. rocky shore 

 sampling program, thermal stress was a source of mortality only at Fox Island-Exposed, and only after 

 the opening of a second quarry cut in August 1983. Barnacle mortality was one of the changes observed 

 in the rocky shore community near the MNPS discharge following the opening of the second cut; the 

 changes are described and discussed in Appendix IV. Briefly, changes in water circulation patterns allowed 

 incursion of warm water to areas that were previously unimpacted (Fox Island-Exposed and the shoreline 

 between FE and the MNPS discharges). In spring, when ambient water temperatures were below 5 °C, 

 the thermal incursion was not detrimental to barnacles; at the time of peak barnacle settlement, maximum 

 temperatures at FE were ca. 12-14 °C. In March and April, dense bamacle set and rapid growth were 

 observed. However, in autumn, water temperature at FE exceeded 28 °C (see earlier Temperature Data 

 section), and barnacles were eliminated from this site. 



Fucus vesiculosus is another important component in the northern Atlantic and local rocky shore 

 communities (Fig. 7). Peak abundance during the year usually occurs in late summer, following growth 

 of germlings that appear in spring; substratum coverage declines as plants are lost to autumn and winter 

 storms. There is also station-to-station variability in Fucm abundance; some stations have very low Fucus 

 cover (e.g., BP), others have consistently high cover (e.g., WP, SE). These patterns are related to degree 

 of exposure to waves; moderately exposed stations favor Fucus populations (Topinka et al. 1981). Fucus 

 cover also varies from year to year. At some stations (e.g., GN, FS), there appears to be a 3-5 year cycle 

 of Fucus abundance, related to the ecological life-span of this alga. Fucus does not propagate vegetatively 

 from a basal holdfast; rather, it occupies new substrata following settlement of zygotes and growth of 



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